Register/MCRegister: Add conversion operators to avoid use of implicit convert to unsigned. NFC

[dsanders]

Summary

This has no functional effect but makes it more obvious which parts of the
compiler do not use Register/MCRegister when you mark the implicit conversion
deprecated.

Implicit conversions for comparisons accounted for ~20% (~3k of ~13k) of
the implicit conversions when I first measured it. I haven't maintained
those numbers as other patches have landed though so it may be out of date.

[arsenm]

llvm/include/llvm/CodeGen/Register.h

127–128

Why are both the signed and unsigned versions necessary?

[dsanders]

llvm/include/llvm/CodeGen/Register.h

127–128

For the unsigned case, it's because it can't tell which operator to use for MCRegister == unsigned. It can do either:

• MCRegister::operator==(*this, MCRegister(Other))
• or, unsigned::operator==(unsigned(*this), Other)

For the signed case, it's the same problem but the operator==(MCRegister, unsigned) is also a candidate

https://godbolt.org/z/8JMcTs

[arsenm]

LGTM

[stella.stamenova]

The windows bot for LLDB is still broken after the partial fix for the breakage:

http://lab.llvm.org:8011/builders/lldb-x64-windows-ninja/builds/7472

[dsanders]

In D65678#1615724, @stella.stamenova wrote:

The windows bot for LLDB is still broken after the partial fix for the breakage:

http://lab.llvm.org:8011/builders/lldb-x64-windows-ninja/builds/7472

Sorry about that. I thought I'd pushed a revert of both commits about an hour ago but I hadn't noticed that terminal was waiting for my password.

[dsanders]

llvm/include/llvm/CodeGen/Register.h

127–128

It turns out MSVC needed one for unsigned short (MCPhysReg) too. That change has been made in the re-commit (r367965) but I should mention that I also moved MCPhysReg's declaration to MCRegister.h so that it can use the real name.

llvm/include/llvm/CodeGen/Register.h

public:
 
   operator MCRegister() const {
     return MCRegister(Reg);
   }
 
   bool isValid() const {
     return Reg != 0;
   }
+
+  /// Comparisons between register objects
+  bool operator==(const Register &Other) const { return Reg == Other.Reg; }
+  bool operator!=(const Register &Other) const { return Reg != Other.Reg; }
+
+  /// Comparisons against register constants. E.g.
+  /// * R == AArch64::WZR
+  /// * R == 0
+  /// * R == VirtRegMap::NO_PHYS_REG
+  bool operator==(unsigned Other) const { return Reg == Other; }
+  bool operator!=(unsigned Other) const { return Reg != Other; }
+  bool operator==(int Other) const { return Reg == unsigned(Other); }
+  bool operator!=(int Other) const { return Reg != unsigned(Other); }
 };
 
 // Provide DenseMapInfo for Register
 template<> struct DenseMapInfo<Register> {
   static inline unsigned getEmptyKey() {
     return DenseMapInfo<unsigned>::getEmptyKey();
   }
   static inline unsigned getTombstoneKey() {

llvm/include/llvm/MC/MCRegister.h

public:
 
   operator unsigned() const {
     return Reg;
   }
 
   bool isValid() const {
     return Reg != 0;
   }
+
+  /// Comparisons between register objects
+  bool operator==(const MCRegister &Other) const { return Reg == Other.Reg; }
+  bool operator!=(const MCRegister &Other) const { return Reg != Other.Reg; }
+
+  /// Comparisons against register constants. E.g.
+  /// * R == AArch64::WZR
+  /// * R == 0
+  /// * R == VirtRegMap::NO_PHYS_REG
+  bool operator==(unsigned Other) const { return Reg == Other; }
+  bool operator!=(unsigned Other) const { return Reg != Other; }
+  bool operator==(int Other) const { return Reg == unsigned(Other); }
+  bool operator!=(int Other) const { return Reg != unsigned(Other); }
 };
 
 // Provide DenseMapInfo for MCRegister
 template<> struct DenseMapInfo<MCRegister> {
   static inline unsigned getEmptyKey() {
     return DenseMapInfo<unsigned>::getEmptyKey();
   }
   static inline unsigned getTombstoneKey() {